1. Field of the Invention
The present invention relates to a process for the preparation of a color filter substrate suitable for use in color liquid crystal display devices.
2. Related Background Art
With the advancement of personal computers, particularly, portable personal computers in recent years, the demand for liquid crystal display devices, particularly, color liquid crystal display devices tends to increase. It is however necessary to reduce the cost of the color liquid crystal display devices for further spreading them. There is an increasing demand for reduction in the cost of color filters particularly given much weight from the viewpoint of the cost.
Various processes have heretofore been attempted for meeting the above demand while satisfying properties required of the color filters. However, no process satisfying all the required properties is yet established under the circumstances. The typical production processes of color filters will hereinafter be described.
The first method is a pigment dispersing process. In this process, a layer of a photosensitive resin, in which a pigment has been dispersed, is first formed on a base and then subjected to patterning, thereby obtaining a pattern of a single color. This process is repeatedly performed three times, thereby forming a color filter composed of colored patterns of R (red), G (green) and B (blue).
The second method is a dyeing process. In the dyeing process, a water-soluble polymeric material, which is a material to be dyed, is applied to a base, and the coating film thus formed is patterned in the desired form by a photolithographic process. Thereafter, the base on which the coating film has been patterned is immersed in a dye bath to obtain a colored pattern. This process is repeatedly performed three times to form a color filter composed of colored patterns of R, G and B.
As the third method, there is an electrodepostion process. In this process, a transparent electrode is first patterned on a base. The base is then immersed in an electrodeposition coating fluid containing a pigment, a resin, an electrolytic solution and the like to electrically deposit the first color. This process is repeatedly performed three times, thereby forming a color filter layer composed of colored patterns of R, G and B. Finally, this color filter layer is calcined to form a color filter.
The fourth method is a process in which pigments are separately dispersed in a thermosetting resin, the resultant thermosetting resin dispersions of R, G and B colors are separately applied to a base by repeating printing three times, and the resin portions thus applied are then thermoset to form a layer composed of colored patterns of R, G and B, thereby forming a color filter.
It is general to form a protective layer on the colored layer in each process.
The need of repeating the same process three times to form the colored patterns of R, G and B is common to these processes. Therefore, the production cost is necessarily increased. There is also offered a problem that a yield is reduced as the number of processes increases. Besides, in the electrodeposition process, formable patterns are limited. It is hence difficult to apply this process to a TFT color liquid crystal display device in the existing technique. Further, the printing process involves a drawback that resolution is poor, and is hence unfit to form fine-pitch patterns.
In order to eliminate these drawbacks, processes for producing a color filter by using an ink-jet system have been proposed in Japanese Patent Application Laid-Open Nos. 59-75205, 63-235901, 1-217320, etc. However, these processes using the ink-jet system are yet insufficient.
In particular, the following problems arise upon the production of a color filter according to the ink-jet printing system.
(1) Color mixing at boundaries between adjacent pixels of different colors; and
(2) Blank areas occurred at boundaries between colored portions and black matrices, and color irregularity caused by the distribution of optical density in colored pixels.
A method for preventing the color mixing at boundaries between adjacent pixels in a color filter has been proposed in Japanese Patent Application Laid-Open No. 4-123005. This method is a method in which a pattern of silicone rubber having high water and oil repellency is formed on black matrices to prevent color mixing in an ink-jet method or printing method. However, this method requires two coating steps, since the pattern of the silicone rubber is formed on a photosensitive resin layer, and the silicone rubber layer or the silicone rubber layer and the photosensitive resin layer are then removed by photolithography, and is hence disadvantageous from the viewpoint of production process.
Therefore, a process for more simply obtaining black matrices having high water and oil repellency at their surfaces has been proposed in Japanese Patent Application Laid-Open No. 7-35916. This process comprises the steps of forming a light-transmissive photosensitive resin layer containing fine silicone particles on a member for forming black matrices, patterning the photosensitive resin layer by photolithography and then processing the member for forming black matrices using the patterned photosensitive resin layer as a mask.
However, since the silicone is contained in a state of fine particles in the thermoplastic resin, this proposal involves the following problems:
(1) the fine silicone particles are left as a residue after development and transferred to the member for forming black matrices, and so defects are caused in the resulting black matrices; and
(2) since the resolution of the photosensitive resin is deteriorated if the amount of the fine-silicone particles added is increased, this process is unfit to form fine-pitch patterns.
As a method for preventing bleeding between pixels using a photosensitive silicone, Japanese Patent Application Laid-Open No. 63-66501 describes a process in which matrices are formed with a photosensitive resin, the top areas thereof are colored black by printing to form black matrices, and a protective film is then formed on the black matrices with the photosensitive silicone. An object of this process is to define boundaries between the black matrices and pixels provided at apertures defined by the black matrices to prevent the occurrence of bleeding between the pixels, thereby producing a color filter with high contrast. However, this process involves a problem that since even edge parts of the black matrices formed with the photosensitive resin are covered with the photosensitive silicone, blank areas occur at boundaries between the colored portions (pixels) and the black matrices.